Assign R / S configuration at each stereogenic centre in the following molecules :
(a) (b)
(c) (d)
(e) (f)
(g) (h)
(i) (j)
(k) (l)
(m)

Question

Assign R / S configuration at each stereogenic centre in the following molecules : (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m)

TestHub · Accepted Answer

Assign CIP priorities at each stereogenic centre, then trace 1 $\to$ 2 $\to$ 3 with the lowest priority group pointing away (invert the result when it points towards you).

(a) Br (1) $>$ OH (2) $>$ CH₂Br (3) $>$ CO₂H (4) : S.

(b) OH (1) $>$ CH₂C(=O) side (2) $>$ CH₂CH₂O side (3) $>$ CH₃ (4) : R.

(c) N (1) $>$ CO₂H (2) $>$ ring CH₂ (3) $>$ H (4) : S.

(d) sp2 ring carbon (1) $>$ sp3 ring carbon (2) $>$ (CH₂)₃CH₃ (3) $>$ H (4) : S.

(e) SiPh₃ (1) $>$ O (2) $>$ Ph (3) $>$ CH₃ (4) : R.

(f) OH (1) $>$ C(=O) side (2) $>$ C(CH₃)₂ side (3) $>$ H (4) : R.

(g) NH₂ (1) $>$ CO₂H (2) $>$ bridgehead carbon (3) $>$ CH₂ (4) : R.

(h) CCl₂ side (1) $>$ CH₂ side (2) $>$ CH₃ (3) $>$ H (4) : S.

(i) At each centre : Cl (1) $>$ CH(Cl)... side (2) $>$ alkyl (3) $>$ H (4) : 2R, 3R.

(j) At each centre : Cl (1) $>$ ring-chain CH₂ side (2) $>$ CH₃ (3) $>$ H (4) : 2S, 4R.

(k) Same priorities as (j) : 2S, 4S.

(l) At each centre : F (1) $>$ CH(F) side (2) $>$ CH₂ side (3) $>$ H (4) : 1R, 2R.

(m) At each centre : I (1) $>$ CH(I) side (2) $>$ CH₂ side (3) $>$ H (4) : 1R, 2S.

Ans. (a) S (b) R (c) S (d) S (e) R (f) R (g) R (h) S (i) 2R, 3R (j) 2S, 4R (k) 2S, 4S (l) 1R, 2R (m) 1R, 2S

Chemistry - STEREO ISOMERISM Question with Solution | TestHub

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